1. Field of the Invention
This invention relates to joinder of plastic conduit to other conduit. More particularly, this invention relates to method and apparatus for effecting joinder of plastic conduit, or pipe, to other conduit, or pipe, such as of different material.
2. Description of the Prior Art
The prior art has seen the introduction of a wide variety of different types of conduits and method of joining of the conduits, whether they were the same or of dissimilar materials. A large improvement in plumbing technology was made when copper pipe began to be employed. The price of copper has risen so dramatically, however, that it is economically infeasible in many applications. Its successor was plastic which had some advantages even over the copper pipe and was more economical. One recent innovation that is seeing increasingly widespread use is the use of plastic conduit such as butylene pipe, or tubing, in low pressure applications.
One of the problems that has plagued the industry has been joinder of the plastic pipe to the other types of conduit, such as the wrought iron pipe, frequently employed in home construction. The prior art has seen different approaches ranging from use of ferrule fittings to the use of preformed ends to be joined with the plastic pipe, such as described in U.S. Pat. No. 3,831,983, the closest art of which I am aware. In that patent, the preformed end is fused onto the end of the plastic conduit and thereafter forced interiorly of and in swaging relationship with carefully preformed shoulders to form a seal. While this method has advantages over the prior art, it was relatively expensive, since the fittings had to be so carefully prepared. Also, application in the field required stocking a relatively complete range of sizes that had been carefully prepared at the factory.
Additional references include the U.S. Pat. Nos. 1,951,860 and 3,687,492, as well as British patent 877,735 and East German document number 57253. U.S. Pat. No. 1,951,860 is a method for making unions for metal tubing and is not really very pertinent. U.S. Pat. No. 3,684,492 does disclose the use of folded plastic tubing ends in forming a service pipe coupling joint that is really not very pertinent to the method of this invention. The British Pat. No. 877,735, however, is much more pertinent to the broad aspects of merely heating the end of the tube and forming an integral washer with the tubing wall. It does not, however, show or make obvious the improved concept of forming the shaped piece in the washer cavity so as to prevent breakage of the tubing near the heating line and to provide an inherent springingness that prevents loosening of fittings. Similarly, the East German patent does not anticipate or make obvious the method of this invention, as defined by the appended claims.
Thus, it can be seen that the prior art has not been totally successful in providing an inexpensive method or apparatus for effecting joinder of plastic conduit to other conduit while retaining the sealing, the preventing of breakage of the conduit adjacent the heating line and providing the inherent springingness needed to prevent loosening of a fitting used; and otherwise obviating the disadvantages of the prior art structure.